1996 BMW 318 Is it a gasket?

Engine Cooling problem
1996 BMW 318 4 cyl Two Wheel Drive Automatic 200k miles

I have a 1996 bmw 318ti. The weather recently dropped down to the teens overnight, and this afternoon I had to go pick my brother up from work. While sitting at a stoplight I heard a pop and then steam started pouring out of my hood and noticed the temp gauge was in the red. I took off the radiator cap (which was tight) and the coolant was almost gone. I tried refilling it but it just leaks out the back of the engine, towards the firewall. There is no lack of power when I drive but the heater blows cold. Is this a significant problem or is it possible pressure just caused a hose to come off?